The production of molecular hydrogen (H-2) from water by hydrogenase of thermophilic cyanobacterium Synechococcus sp. strain H-1 has been studied by following the time courses of the hydrogen concentration in the gas-phase, cell mass concentration and cellular content of D-glucose in dark batch reactions at temperatures ranging from 313 to 333 K. An anaerobic, dark, NO3- starvation, neutral or alkaline pH and shaking condition was found to be a prerequisite for H-2 production. Strain H-1 could multiply and produce hydrogen at all temperatures studied. A linear relation between hydrogen production and glucose consumption was observed and the yield coefficient of hydrogen in terms of D-glucose consumption was 71, 115 and 146 at initial concentrations of cell mass of 0.75, 2.5 and 9.5g.L-1, respectively. The activation energies for the maximum specific rates of cell mass growth, D-glucose consumption and hydrogen production were found to be 62, 12.6 and 122 kJ.mol(-1), respectively. The maximum specific hydrogen production rate was found to be 0.09 mu mol.mg-chl a(-1).h(-1) at 328 K, which is comparable to that reported in non-nitrogen-fixing unicellular cyanobacteria. It is concluded that utilization of thermophilic Synechococcus sp. strain H-1 for hydrogen production is beneficial since the contamination risk of mesophilic bacteria is low.